Several closely related projects are presently ongoing to investigate normal motor control in the hand and the restoration of motor and sensory function in the hands and arms by functional neuromuscular stimulation (FNS). This program consists of several interrelated projects involving basic scientific and clinical research, and clinical evaluation of neuroprostheses with disabled individuals. Inherent muscle mechanical properties and the reflex alteration of these properties are being assessed in normal subjects to provide models of the neural control of hand function. The results of these studies will be valuable in assessing the validity of the current hypothesis that muscle stiffness is regulated by reflexes and will provide foals for the restoration of hand function by FNS. Research on the restoration of motor function in paralyzed extremities is carried out in several areas. The first area is the restoration of grasp and release using FNS. With electrical stimuli applied by way of intramuscular electrodes, functional hand control can be established. NIH is funding an investigation of the repeatability of open loop control of hand position and force, and research on the design of closed loop control systems for regulating the input-output properties of electrically stimulated muscles to provide enhanced performance. The second area is the development of new command-control sources (such as shoulder and wrist position) to provide methods for paralyzed individuals to control their active orthoses or prostheses. The third area is NIH supported research for the development of externally worn position and force sensors to be used in both the closed loop control systems described above, and for providing artificial sensation by stimulation of skin with intact sensation. The proposed motion study system will be used as an integral component of each of these projects. The projects have a common need for accurate measurement of the position in space of the elements of the upper extremity. In most applications, the information is processed in real time and used in a control (or feedback control) process. The availability of the Selspot II system would reduce or eliminate the substantial development time needed for fabrication of special purpose physical transducers and thus enable us to orient our investigations on the mechanisms of normal motor control and the enhancement of motor and sensory performance of the paralyzed extremity.